Secondary batteries are a type of rechargeable battery in which ions move between the anode and cathode through an electrolyte. Secondary batteries include lithium-ion, sodium-ion, potassium-ion batteries, and lithium batteries as well as other battery types. Secondary batteries are often made of many cells that are grouped together to form the battery. Each cell of a secondary battery contains an electrolyte, and at least one cathode, and at least one anode. When the cells are grouped together to form a battery, the cathodes and anodes of each cell can be electrically coupled to achieve the desired capacity of the battery.
In secondary battery cells, both the anode and cathode comprise materials into which a carrier ion inserts and extracts. The process of the carrier ion moving into the anode or cathode is referred to as insertion. The reverse process, in which the carrier ion moves out of the anode or cathode is referred to as extraction. During discharging of a cell, the carrier ion is extracted from the anode and inserted into the cathode. When charging the cell, the exact reverse process occurs: the carrier ion is extracted from the cathode and inserted into the anode.
Lithium-ion batteries are a popular type of secondary battery in which the carrier ions are lithium ions that move between the cathode and the anode thought the electrolyte. The benefits and the challenges of lithium-ion battery cells are exemplary of the benefits and challenges of other secondary battery cells; the following examples pertaining to lithium-ion battery cells are illustrative and are not limiting. In lithium-ion battery cells, the lithium ions move from the anode to the cathode during discharge and from the cathode to the anode when charging. Lithium-ion batteries are highly desirable energy sources due to their high energy density, high power, and long shelf life. Lithium-ion batteries are commonly used in consumer electronics and are currently one of the most popular types of battery for portable electronics because they have high energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. Lithium-ion batteries are growing in popularity for in a wide range of applications including automotive, military, and aerospace applications because of these advantages.
FIG. 1 is a cross section of a prior art lithium-ion battery cell. The battery cell 15 has a cathode current collector 10 on top of which a cathode 11 is assembled. The cathode 11 is covered by a separator 12 over which an assembly of the anode current collector 13 and the anode 14 is placed. The separator 12 is filled with an electrolyte that can transportions between the anode and the cathode. The current collectors 10, 13 are used to collect the electrical energy generated by the battery cell 15 and connect it to other cells and to an outside device so that the outside device can be electrically powered and to carry electrical energy to the battery during recharging.
For most existing secondary batteries, after the initial charge there is a significant drop in total overall capacity. For instance, in a standard lithium-ion battery, the loss in total charge capacity after the first charge-discharge cycle is about 5-15%. The term “about” as used herein means within plus or minus 15% of the specified value. Moreover, a portion of the capacity of most existing secondary batteries is lost with each subsequent charge-discharge cycle. For instance, in a standard lithium-ion battery, the loss in total charge capacity after each subsequent charge-discharge cycle is about 0.1%.
Three dimensional energy battery cells and batteries can produce higher energy storage and retrieval per unit geometrical area than conventional two dimensional (or planar) devices. Three-dimensional secondary batteries also have a decided advantage in providing a higher rate of energy retrieval than planar counterparts for a specific amount of energy stored, by means such as minimizing or reducing transport distances for electron and ion transfer between an anode and a cathode. These devices can be more suitable for miniaturization and for applications where a geometrical area available for a device is limited and where energy density requirement is higher than what can be achieved with a planar device. A three-dimensional secondary battery cell can be one in which any one (or more) of an anode, a cathode, and a separator are non-planar in nature, and an actual surface area for such non-planar component is greater than twice its geometrical surface area. In some instances, a separation between two height planes on a third dimension should be at least greater than a periodicity in an x-y plane divided by a square root of two. For example, for a 1 cm×1 cm sample, a geometrical surface area is 1 cm2. However, if the sample is not flat but has a groove in a depth dimension whose depth is greater than one divided by the square root of two, or 0.707 cm, then its actual surface area would be greater than 2 cm2.